JPH0383462A - Device for measuring light scattered by information support - Google Patents

Abstract

PURPOSE: To measure the light which is scattered by an information supporter even when the exposed part of the supporter is smaller than the field of view of a sensor and the distance between an objective lens and the information supporter varies in a 80 to 120% range by locating the supporter at the rear side of the objective lens so as to keep the quantity of light incident on the photosensitive surface of the sensor within a 5% range. CONSTITUTION: A photosensitive sensor 8 is placed in an optical path that is set between a focusing lens 6 and an image forming point 7 that is set before the focal point (f) of the lens 6. The entire photosensitive surface of the sensor 8 is included in the light beam that is focused at the point 7 as the result of the lens 6. The optimum position of the sensor 8 is decided at a point that is distant from the lens 6 by 7.9mm as long as the distance is set a 1cm between an information supporter 2 and the lens 6 together with the focal distance set at 8mm, the effective square photosensitive area of the sensor 8 set at 4mm<2> and the diameter of the lens 6 set at 50mm respectively. Under such conditions, the quantity of light incident on the sensor 8 is kept within a 0.2% range and substantially constant even though the distance between the supporter 2 and the lens 6 varies within a 0.8 to 1.2cm range.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring light scattered by an information support, said apparatus comprising a light source usable for exposing a part of the information support and a light-sensitive a sensor having a surface and providing an output signal in response to the amount of light falling on the photosensitive surface; and a sensor disposed between the information support (2) and the information support; The exposed area is smaller than the field of view of the sensor.

The device made based on the above is US-^-463960
7, which describes a paper edge detector in which a light beam is directed onto a small portion of a reflective surface. In this case, the specular light from this reflective surface passes through a converging lens and impinges on the detector. Within a certain range, the amount of light detected is independent of the orientation of the reflective surface, as long as the distance between this exposed part and the converging lens remains constant.

A device of this type can be used, for example, to measure the exposure required for backgroundless copying in an electrophotographic device. For this purpose, the amount of light scattered by the information support is measured by exposing a part of this support to light and measuring the amount of light scattered from the exposed part;

A disadvantage of this type of device is that if the distance between the information support (2) sensor changes, the amount of light falling on the sensor may change. This occurs, for example, when the information support moves along a path along the sensor, with the possibility that the positioning of the information support relative to the sensor varies.

The aim of the invention is to significantly reduce the above-mentioned disadvantages. According to the invention, this object is realized in a device as mentioned at the beginning of the description. In this device, the distance between the sensor information support (2) is 80 to 120 of this distance.
The sensor is located some distance behind the objective lens such that the amount of light hitting the photosensitive surface of the sensor remains constant within 5% when varying over a length of 5%. It is placed with The maximum length dimension of the photosensitive surface of the sensor satisfies the following equation:

In the above equation, A represents the distance between the information support and the sensor, and B
represents the distance between the sensor and the photosensitive surface of the sensor, f represents the focal length of the objective lens, and d represents the effective diameter of the objective lens.

(2) No matter how the distance between the sensors changes within a wide range, the amount of light on the photosensitive surface of the sensor remains constant or remains substantially constant. It has been found that there is an optimal position for the sensor. This optimum position depends inter alia on the distance between the information support (2) sensors, on the focal length of the objective lens, on the size and shape of the photosensitive surface of the sensor, and on the scattering properties of the information support.

In some implementations, it is possible to calculate the optimal position of the sensor if the above parameters are known. However, in many cases, this calculation is very complex, and in practice it is easier to determine the optimal position by experiment. The following procedure can be adopted for this purpose.

That is, this procedure involves placing the sensor behind the objective lens at a distance of, for example, 110% of the focal length of this lens, and ensuring that the amount of light incident on the sensor remains constant or substantially constant. Measuring the output signal of the sensor as a function of the displacement of the information support relative to the objective lens over the length required to remain unchanged, as well as stepping the sensor in the direction of the objective lens. It consists of moving and measuring the output signal of the sensor as a function of the displacement of the information support with respect to the objective lens over the required length for each step of the movement.

In this way, it is easy to obtain a sensor position such that even if the information support is displaced relative to the objective lens, the amount of light incident on the sensor remains constant to a degree sufficient for the required application. It is determined.

It has been found that it is possible to calculate the optimal position of the sensor if the information support scatters light diffusely and the length and width of the sensor photosensitive surface are equal or substantially equal to each other. has been done. Information support (2) The distance A between the sensors and the distance between the sensor and the photosensitive surface of the sensor, the focal length f of the objective lens, and the size M of the sensor photosensitive surface are: If chosen to satisfy or substantially satisfy the following equation, the amount of incident light on the sensor remains substantially constant, even when displacement of the information support relative to the objective lens occurs.

If A, M and f are known, it is possible to calculate the sensor position B based on the above equation. Also, for example, if sensors of different shapes are used or if the information carrier does not scatter the light completely diffusely,
This calculated sensor position can be used as a starting value for experimental optimization of sensor position as described above.

Other features and advantages of the invention will become clearer from the following description made with reference to the accompanying drawings.

Figure 1 shows one embodiment of a device according to the invention that can be used to measure the amount of scattered light as transmitted light from an information support that scatters the light completely diffusely. In that device, light is focused onto an information support 2 by a light source l. For this purpose, a pinhole 3 is placed in the vicinity of the light source l.

The light from the resulting point source is imaged onto a small surface 5 of the information support 2 via a converging lens 4 . The diffusely scattered light from the information support 2 is imaged onto a point 7 by an objective converging lens 6 . The photosensitive sensor 8 is arranged in the optical path between the converging lens 6 and an imaging point 7 in front of the focal point f of the converging lens 6. The position of the sensor 8 is such that no matter how much the distance between the information support 2 and the converging lens 6 changes within a few degrees, the amount of light falling on the sensor 8 remains essentially constant. selected. The entire photosensitive surface of sensor 8 is located at point 7 as a result of lens 6.
It falls within a light beam that converges at . Information support 2
and the converging lens 6 is 10, and the focal length is 8.
If the square effective photosensitive area of the sensor 8 is 4 and the diameter of the converging lens is 50011, then the optimal sensor position is 7.9Iff11 away from the lens 6. At this time, the information support 2 and the converging lens 6
The amount of light falling on the sensor 8 is 0.2% no matter how the distance between the
remains essentially constant within the range of .

In the above embodiment, when the distance between the sensor 8 and the lens 6 is a value other than the above-mentioned value, the sensor 8
The constancy of the amount of light hitting the top becomes much worse.

The percentage change in the amount of light on the sensor 8 as a function of the distance between the lens 6 and the sensor 8 when the distance between the information support 2 and the lens 6 varies over a length 4 nn is determined by the second As shown in the figure. FIG. 2 shows that when the distance between the information support 2 and the lens 6 is varied over a length of 4 m, the sensor 8 moves away from the optimum sensor position (either closer to the lens 6 or further away from the lens 6). It is also shown that a shift of one loaf changes the amount of light on the sensor 8 by about 12%.

FIG. 3 shows another embodiment in which the device according to the invention is used to measure the amount of scattered light as reflected light from an information support 12, in which the information support 12 is
It is positioned in a path 19 through which the information support 12 is fed through the device. During the measurement, the information support 12 is located between the boundaries 20 and 21 of said path 19, so that the distance between the information support 12 and the objective lens 16 is equal to the boundaries 20 and 21 of the path 19. It is possible to vary within a range.

A light source 11 provided with a pinhole 13 illuminates a small portion of the information support 12 with incident light.

For this purpose, the light is focused in the center of path 19 by lens 14 . The distance between the information support 12 and the converging lens 16 is 1 am, the focal length is 1OI6n, the square effective photosensitive area of the sensor 18 is IO-,
If the lens diameter is 50 mm, the optimal sensor position is 9.7 mm away from the lens 16.

The change in distance between the information support 12 and the converging lens 16 is 1
Within the range of 8 to 1.2 am, the amount of light on the sensor 18 remains constant within the range of 1.2 am. Under these conditions, the angle between the optical axis of the illumination path and the optical axis of the measurement path is 25°. When the information support 12 is moved out of the center of the path 19, the light focal point 15 moves with respect to the optical axis of the measurement path. This greatly affects the amount of light on sensor 18. In order to keep the amount of light on the sensor 18 as constant as possible, the angle between the optical axis of the illumination path and the optical axis of the measurement path should be as small as possible.

However, if the angle is very small, there is a risk that specularly reflected light will hit the sensor 18. The sensitivity to changes in the position of the information support 12 with respect to the lens 16 is determined by the angle 45
Measurements have shown that at an angle of 25° the risk of specular reflection remains low, whereas at an angle of 25° the risk of specular reflection remains low.

FIG. 4 shows another embodiment in which a device according to the invention is used to measure the amount of reflected and transmitted light scattered by an information support 42. FIG. In this case, pinhole 4
A single light source 41 is used, of which 3 is provided in the vicinity. The resulting point source light is transmitted to the information support 42.
is imaged onto a small surface 45 of the information support 42 via a converging lens 44 by focusing the light onto a point in the center of the path H passing through the device.

This embodiment uses a light source 41 and a sensor 48 on the same side (with respect to the information support 42) to measure the amount of reflected light, and an objective converging lens 46 is placed between the sensor 48 and the path 49. Ru. a second for measuring the amount of transmitted scattered light;
A sensor 50 is arranged on the other side of the information support, and a converging lens 51 is arranged between the sensor 50 and the path 49. During the measurement, information support 42 and lenses 46 and 5
1 can vary within the boundaries 52,53 of the path 49.

This embodiment uses a pinhole 43 with a diameter of 1 m. The distance between the centers of the four paths and the objective lens 51 is five degrees. The distance between the center of path 49 and lens 46 is L
Onm. Biconvex lenses 44, 46, and 51 are all to
It has a focal length of +m and a diameter of 50-. sensor 48
, 50 has an effective photosensitive area of 4-. The distance between sensor 50 and lens 51 is 9.2 mm. The distance between sensor 48 and lens 46 is 9.9 m. The change in the distance between the information support 42 and the converging lens 46 and the distance between the information support 42 and the converging lens 51 increases the
If it is within the range of 0-120%, the sensor 48.5G
The amount of light above remains constant within the range of %.

This latter embodiment can be used, for example, in electrophotographic apparatus where particularly translucent originals are to be copied. Optimal exposure and/or proper contrast for suppressing background on the copy can be automatically controlled based on the reflection and transmission properties measured by the apparatus of the invention, if necessary. . In this case, based on measurements of the amount of scattered light that is reflected and transmitted, it is possible to select only incident light exposure, select transmitted light exposure, or select a combination of both. It is also possible to vary the total amount of light and the interrelationship between the incident light lamp intensity and the transmitted light lamp intensity.

In the example described above, the lamp 1, 11.41 together with the pinhole 3□N, 43 is used for exposure and the converging lens 4.14.44 is used for the information support 2. +2.42 and lamp 1, 11.41, so that the light was focused onto the information support 2.12.42. It is possible to project the convergent light onto the information support and the information support 2.
1242 even if a deviation occurs, the information supports 2, 12.
Other light sources that keep the size of the light spot on 42 constant or substantially constant can also be used, such as light emitting diodes, lasers and the like. When used in xerographic equipment to measure the brightness of the background of a document, it is possible to minimize the exposed area so that any information present on the document has minimal effect on the measurement. It is advantageous to make it as small as possible.

It has been found that the presence of folds or wrinkles in the information material, especially when measured in reflected light, is unfavorable in keeping the amount of light measured at a constant value. An apparatus according to the invention as shown in FIGS. 3 and 4, such that the plane delimited by the optical axis of the exposure path and the optical axis of the measurement path is perpendicular to the transport method of the information carrier. It has been found advantageous to position embodiments of the invention. If there is a fold perpendicular to the transport direction of the information carrier, the measurement signal will exhibit gaps when the fold passes through the device.

However, when measuring the exposure required to obtain a background-free copy, the maximum measurement signal is used, so that such creases do not have an adverse effect on the operation of the device.

[Brief explanation of drawings]

FIG. 1 is a diagram showing one embodiment of the apparatus according to the present invention, and FIG. 2 is a diagram showing an information support (2) in the embodiment shown in FIG.
) a graph showing the percentage change in the amount of light on the sensor as a function of the distance B between the sensors as the distance between the sensors varies over a length of 80 to 120% of this distance; FIG. 3 schematically shows a second embodiment of the device according to the invention, and FIG. 4 schematically shows a third embodiment of the device according to the invention. 1, it, 41... light source, 2.123.1
3.43...Pinhole, 4, 6.14.16
．． 44.46.51... Convergent lens, 8, 18
．． 48.50...Photosensitive sensor, 9, 19.4
9...Information support path, 20, 2152.53
・・・・・・Boundary of information support path, 5, 15.45・
...A small surface of an information support. 42...Information support, it1 person #! Uesaka FIG, 1 1111-B (mm 1 F! 6.2 \ years old

Claims (2)

[Claims] (1) An apparatus for measuring light scattered by an information support, the apparatus comprising: a light source usable to expose a portion of the information support; and a light-sensitive surface; a sensor that provides an output signal based on the amount of light falling on the sensor; and an objective lens disposed between the information support and the sensor, the exposed portion of the information support being smaller than the field of view of the sensor; The amount of light striking the photosensitive surface of the sensor remains constant within 5% even when the distance between the objective lens and the information support varies over a length of 80-120% of this distance. The sensor is placed at some distance behind the objective so that it remains unchanged, and further, where A represents the distance between the information support and the objective. the photosensitive surface of the sensor, where B represents the distance between the objective lens and the photosensitive surface of the sensor, f represents the focal length of the objective lens, and d_l_e_n_s represents the effective diameter of the objective lens. The maximum length dimension L of the surface is determined by the equation, L<[fA+fB-AB]/[fA]・d_l_e_n
A device for measuring light scattered by an information support, characterized in that it satisfies _s. (2) the length and width of the photosensitive surface of said sensor are equal or substantially equal to each other, and further the distance A between said information support and said objective lens and the photosensitivity of said objective lens and said sensor; The distance B to the surface, the focal length f of the objective lens, and the size M of the photosensitive surface are determined by the equation 2√2/π・AM/(M+4A^2)√[M+2A^2
]=fB/fA+fB-AB・[1-4/π・arcs
in(√2·A)/(√M+4A^2)]. equipment for.